What do the different opentelemetry features actually do?

[BatmanAoD]

The documentation says:

Optionally enable opentelemetry integration by enabling an opentelemetry version feature

Are the features all orthogonal? (I.e. is it safe to enable multiple versions?) What happens if the version of the OTEL library used in the rest of the code doesn't match the feature(s) enabled?

Does a feature flag for version 0.31 need to be added?

[masongup-mdsol]

The Rust OpenTelemetry crates have a bunch of global magic for keeping track of the current tracing information. Having this work correctly is dependant on everything in the codebase using the same single version of the OpenTelemetry crates.

If you're running a web server with OpenTelemetry Tower middleware on the server, an OpenTelemetry sender task, a logging setup making use of the OpenTelemetry tracing info, and using this Reqwest middleware to put tracing information on your outgoing requests, then having the same OpenTelemetry crate version for all of those things lets the tracing information be consistent through all of those parts. If any of them are different, then those various parts may get their own independent traces which are disconnected from everything else.

[BatmanAoD]

Thanks! Is it safe to have multiple of the features enabled, and do you know what needs to be done to add a flag for 0.31?

[masongup-mdsol]

Is it safe to have multiple of the features enabled

I think short version is no. I'm not completely sure what it would do. I doubt it would cause panics, but it seems likely it will cause something in trace propagation to not work properly.

do you know what needs to be done to add a flag for 0.31?

There's already a PR for it.

As near as I can tell, there isn't a big change in the OpenTelemetry crates between 0.30 and 0.31, so you're not losing much for now by keeping all OpenTelemetry-related crates in your project at 0.30.